Frequency dividers are commonly used to produce lower-frequency signals from higher-frequency signals. Frequency dividers are important building blocks of electronic circuits. In some electronic circuits, a frequency divider constitutes part of a phase-locked loop (“PLL”) or another frequency-generating electronic circuit. Generally, a PLL is a circuit that permits an external reference signal to control the frequency and phase of a signal generated by a frequency source that is part of the PLL.
Some PLL circuits include a voltage-controlled oscillator (“VCO”), a phase detector, and a filter. In such PLL circuits, the frequency of the VCO is the same as the frequency of the external reference signal. Other PLL circuits additionally include a frequency divider. In such PLL circuits, the frequency of the VCO is a multiple of the external reference signal. As an example, a frequency synthesizer having a PLL that includes a frequency divider and in which the external reference signal is provided by a crystal oscillator, will derive output signals at different frequencies from the signal generated by the VCO. The signal generated by the VCO is referenced to the external reference signal. The frequency synthesizer output signals will have the same frequency stability as the external reference signal provided by the crystal oscillator.
Unfortunately, while frequency dividers are advantageous for producing signals with different frequencies, the signals they produce tend to have a higher noise level than the original signal because frequency dividers impose significant jitter on the transitions of the signals they produce. Such signals therefore exhibit high levels of phase noise. Therefore, there is a need for a reduced noise frequency divider system and reduced-noise frequency divider method.